1. Field of the Invention
This invention relates generally to lithium ion batteries, and more specifically to novel block copolymers and method for their preparation, which copolymers exhibit simultaneous electronic and ionic conductivity, these copolymers having particular suitability for use with battery electrodes.
2. Brief Description of the Related Art
Increasing the energy density of rechargeable lithium batteries is a goal of considerable significance.(1, 2) While most of the efforts thus far have focused on the energy producing components of the battery,(1-7) i.e. the active components in the electrodes that participate in the energy-producing redox reactions, improvements in the non-energy-producing battery components are essential if these targets are to be met.
Current lithium-lot batteries contain several non-energy-producing components: (1) a liquid electrolyte to transport ions between the electrodes, (2) a polymeric separator to prevent contact between the electrodes, (3) an inactive polymer that binds the active particles in the electrodes, (4) an electronic conductor such as carbon to conduct electrons within the electrode, and (5) current collectors that deliver electrons to the external circuit. The non-energy producing components account for about 50% of the mass of a weight of a lithium battery.
Redox reactions that occur at the electrodes of batteries require transport of both ions and electrons to the active centers. This is challenging because the materials that are usually used to transport the two species are very different. Electrons are usually transported in crystalline solids such as metals or semiconductors while ions are transported in aqueous or organic salt solutions. In lithium batteries, electronic conduction is enabled by the introduction of carbon, white ion conduction is enabled by the creation of a porous structure that is backfilled with an organic electrolyte.(8)
Identifying processing steps that lead to the presence of active materials at the junctions of the electron- and ion-conducting phases is non-trivial. While it has been recognized that mixed conductors, i.e. materials that transport both ions and electrons to active sites would be useful, synthesizing materials capable of transporting both species and demonstrating success in executing redox reactions has not yet been accomplished.